Flex Design Basics
Fl Design
Flex
D i Basics
B i
Application Types:
–Static: Not meant to flex
–Flex to Install: Only meant to flex on limited basis. To install or replace
and repair.
–Dynamic: Depending on flex construction and conditions this could
result in >1M flex cycles
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Flex Design Basics
Terminology
•Back Bared Pads / Back Side Access - This is a flex that is typically single sided in
construction but has the copper accessed from both sides.
•Conductor aspect ratio - Relationship of conductor width to conductor height.
General rule of thumb is conductor width should be greater then 5 times the
conductor thickness.
•Coverfilm / Coverlay -This is the insulating material, usually in a film format, that is
laminated to the flex circuit to define solderable areas. Can be drilled, laser cut or chemically
removed to create complex geometries.
•Dynamic –A type of flexible circuit that will see repeated flexing, sometimes more than 1
million cycles, such as in a disk drive, mobile phone or laptop computer.
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Flex Design Basics
Terminology (Continued)
•Hold Down Tabs -These are extensions of the copper pad and are used to help anchor
the p
pad during
g soldering
g processes
p
both in assembly
y and rework.
•I-Beam Effect -This is the result of stacking your conductors during your design.
Subsequent flexing induces stress and compression, causing cracking to occur.
•PIC, Photoimagable Coverfilm / Coverlay -This is another means of defining your solderable
areas. This material is apply in a clean room environment, exposed with an artwork and then
developed. This allows for complex geometries not available from routing or other soft tooling
means.
•PSA (Pressure Sensitive Adhesive) -An adhesive used to bond stiffeners to specific regions of
the flex circuit
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Flex Design Basics
IB
I-Beam
Eff
Effectt
Always try to avoid “stacking traces” in the same location from layer to layer.
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Flex Design Basics
H ld Down
Hold
D
T
Tabs/Pad
b /P d Staking
St ki
Stress from bending/flexing can cause issues with the copper pads maintaining adhesion
to the base material. The addition of copper extending under the coverlay will help
maintain the adhesion of the pads.
Hold Down Tabs
Coverlay Openings
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Flex Design Basics
C l l ti Minimum
Calculating
Mi i
Bend
B d Radius
R di
The general guideline for calculating minimum bend radius is 10X the total thickness of
the flexible circuit for double sided (2 layer) applications.
The general guideline for calculating minimum bend radius is 6X the total thickness of the
flexible circuit for single sided (1 layer) applications.
The general guideline for calculating minimum bend radius is 20X -25X the total thickness
of the flexible circuit for multi-layer (3+ layers) applications.
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Flex Design Basics
M t i l
Materials
9082
9460
9482
Not generally available overseas.
PCB Solutions
S l ti
recommends
d Taiflex
T ifl material
t i l for
f mostt flexible
fl ibl applications,
li ti
due to cost, performance and lead-time overseas.
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Flex Design Basics
For additional information, PCB Solutions recommends the book:
Available for free download at:
http://www.flexiblecircuittechnology.com/
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